This doesn't seem like it should be too difficult, but I've been struggling with this for days. I'm wondering if I'm going about this in the wrong way and if someone else would do it differently.

Here is a picture of the room I am trying to model. It has an inlet that I will patch with a cold/hot airflow, and outlet that I will patch with a zero gradient, and a window that I will patch with a heat gain/loss. Everything else is a wall.

you could also mesh this geometry with 3 blocks in blockMesh, and then create your patches with the faceSet and createPatch utilities... it might be hard to control the exact distribution of the cells as well as the exact extent of the patches, though... for full control you need plenty of blocks, like Alberto says.